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Varicella serology among school age children with a negative or uncertain history of chickenpox |
Lieu T A, Black S B, Takahashi H, Ray P, Capra A M, Shinefield H R, Adler N E |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology Varicella serotesting or presumptive vaccination in school age children with a negative or uncertain history of chickenpox.
Economic study type Cost-effectiveness analysis.
Study population School age (7 to 12 years of age) children making medical visits, whose parents wished varicella vaccination and classified their children as having a negative or uncertain history of chickenpox.
Setting Primary care. The economic study was carried out in San Francisco, USA.
Dates to which data relate The effectiveness data were collected between October 1995 and December 1996. The resource and cost data were extracted from another paper published by the same authors in 1995. No date was given for the prices used.
Source of effectiveness data The evidence for the final outcomes was derived from a single study.
Link between effectiveness and cost data The costing was not performed on the same patient sample as that used in the effectiveness study.
Study sample Power calculations were used to determine the sample size. The exclusion rate was 23%. 2% of parents refused to be interviewed. A total of 1,177 parents of eligible children completed the telephone interviews. A total of 23% of eligible subjects was excluded from the study for various reasons. A total of 2% of subjects refused to participate in the study.
Study design The study was a prospective cohort study, performed in a non-profit, group model health maintenance organisation consisting of 32 clinics in the region. The duration of the follow-up of the study cohort was 12 months.
Analysis of effectiveness It was not stated whether the analysis of the clinical study was based on intention to treat or on treatment completers only. The main outcome measures were serology results (seropositive or seronegative), the rate of 12-month follow-up vaccination for subjects with seronegative results,and parent preference. The study cohort was compared with a group of 247 subjects (whose parents were interviewed) to assess the representativeness of the study cohort. The relationship of seropositivity to age and history was investigated using a logistic regression.
Effectiveness results The seropositive results were as follows: 48% (95% CI: 40 - 56) of children whose parents were not sure of their chickenpox history were seropositive; the corresponding rates for the "probably had not", "definitely had not", "probably had", and "definitely had" children were 32% (95% CI: 26 - 38), 25% (95% CI: 21 - 28), 74%, and 89%, respectively (the range of varicella seroprevalence was from 9 to 68% depending on age and clinical history). Logistic regression revealed that age and history were significantly correlated with the serology results (P<0.001). The proportion of subjects having been exposed to chickenpox generally, or via a household member, was 73% and 20%, respectively. The children having a history of exposure to chickenpox were more likely to have positive results compared to those without such an exposure history (65% versus 35%, P<0.0001). 73% of parents whose children had undergone serotesting preferred serotesting over vaccination.65% of subjects with seronegative results had vaccination during the 12-month follow-up period. There were significant differences between the study cohort and comparison group in terms of a number of outcome variables.
Clinical conclusions The study revealed that seroprevalence depended on age and clinical history. About 50% of subjects with uncertain histories were seropositive. Most of the parents of children having already had serotesting preferred it to vaccination.
Modelling A previously published spreadsheet model was used to combine cost and effectiveness probabilities in order to estimate the cost-effectiveness of serotesting versus presumptive vaccination.
Measure of benefits used in the economic analysis No summary benefit measure was identified in the economic analysis and only separate outcomes (effectiveness) were reported.
Direct costs Resource quantities were not reported separately from the costs. The cost components were not reported separately. The test cost consisted of venipuncture, materials, processing, and clerical cost. The future medical costs resulting from future chickenpox among susceptible patients were included in the cost analysis. The cost analysis was performed from the point of view of a health care provider organisation. No date was specified for the prices used.
Estimated benefits used in the economic analysis No summary benefit measure was introduced.
Cost results The test cost was $8.20 versus $39 for the cost of vaccination.
Synthesis of costs and benefits The cost per chickenpox case prevented was estimated as a measure of cost-effectiveness. The values of the cost-effectiveness ratio were not reported.
Authors' conclusions The authors concluded that "among children 7 to 12 years old with negative or uncertain histories of chickenpox, varicella seroprevalence ranges from 9 to 68% depending on age and clinical history. Patients are generally receptive to serotesting, although individual preferences vary. In the population studied it would be most cost-effective to recommend testing before deciding about vaccination for children 9 to 12 years old with uncertain histories of chickenpox.
CRD COMMENTARY - Selection of comparators The reason for the choice of the comparator is clear.
Validity of estimate of measure of benefit As mentioned by the authors, lack of randomisation might have had adverse effects on the internal validity of the effectiveness measures.
Validity of estimate of costs Resource quantities were not reported separately from the costs. Adequate details of methods of cost estimation were not given. The inclusion of indirect costs would have been appropriate.
Other issues Given the lack of randomisation, sensitivity analysis, and statistical analysis of the costs, the results need to be treated with some caution. The issue of generalisability to other settings/countries was partially addressed by pointing out that the cost-effectiveness results might change dramatically if the analysis was to be carried out for small health care providers not enjoying the economies of scale, and therefore facing a much more expensive serotesting procedure.
Source of funding Supported by the Innovation Program of Northern California Kaiser Permanente, the Vaccine Safety Datalink Project, National Immunization Program, Centers for Disease Control and Prevention and the National Vaccine Program Office.
Bibliographic details Lieu T A, Black S B, Takahashi H, Ray P, Capra A M, Shinefield H R, Adler N E. Varicella serology among school age children with a negative or uncertain history of chickenpox. Pediatric Infectious Disease Journal 1998; 17(2): 120-125 Indexing Status Subject indexing assigned by NLM MeSH Chickenpox /economics /epidemiology /immunology; Chickenpox Vaccine /administration & Child; Cost-Benefit Analysis; Cross-Sectional Studies; Health Maintenance Organizations /economics; Herpesvirus 3, Human /immunology; Humans; Logistic Models; Medical History Taking; Seroepidemiologic Studies; Serologic Tests /economics; Vaccination /economics; dosage /economics AccessionNumber 21998000368 Date bibliographic record published 31/01/1999 Date abstract record published 31/01/1999 |
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